Is 40km/h with a 36t sprocket normal?

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cyclepro101

cyclepro101

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I have a Z80 (66cc) on a mountain bike. I have upgraded to a 0.76mm main jet, cut off the internal pipe on the muffler cover and screwed in a 3/4" socket with a 3/4" extention pipe and I have a few extra holes drilled in the back of the carb cover. I have also reamed out the intake side of the carb a little and had a bit of a go at opening up the muffler flange where it bolts onto the cylinder. I also have a new NGK spark plug cap and wire and use a NGK B**6** plug. I have also put on a 36 tooth sprocket.
Now is 40km/h about what this thing should do flat out? Maybe if I was going down a hill or let it ring out a bit longer I could get 45km/h but I thought it would go a bit faster than this. It pulls pretty good but just wont seen to rev way way way out. It pulls pretty good to about 38km/h then goes back to chugging a bit. I have also only done 350km/s about 3 tanks. Will it loosen up a bit more?

Steve
 
Cabinfever1977

Cabinfever1977

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40kph is 24mph. i can get my bike all stock with a 44t upto 32mph on flat ground and i can do 24mph up a hill. so what ever you did didnt help you any. that 36t spocket should get you up to 35-40mph on a 26" bike. unless you have a smaller bike,what size bike are we talking about?
and no, what ever its running at now is probally what it will do,if that.
 
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cyclepro101

cyclepro101

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Thanks, Thats what I feared. It has std. 26" wheels. Anything I should do or check to get some speed out of this thing?

Steve
 
Cabinfever1977

Cabinfever1977

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what gas/oil ratio are you using?
and maybe you need to move the c-clip on the carb slide.
what speed did it do before changing the sprocket and modifing the other stuff?
a picture of the bike will help a lot.
 
joe-craft

joe-craft

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one of your problems would be your jet size, i tried to change my jet size now its just flooding my enigne and not getting any power, so you should either fix your jet put it back to 70 and try it then.
 
Cabinfever1977

Cabinfever1977

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maybe you should get a new engine and leave it stock and then use your 36t sprocket and you should be able to do 35-40mph+

zoombicycles has engine kits for $109.95 and includes free shipping
 
cyclepro101

cyclepro101

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I question some of the speeds guys on here tsay they are getting. Using this Kart Sprocket Calculator Sprocket Calculator
With 26" wheels and a 10 tooth on front and a 44 or 36 on the rear I am getting correct speeds at 6000 rpm.
Also I did go back to the std jet and it was crap. Starving for fuel at WOT.
Also I will take a photo and post later.
I still say at 300km's its probably not fully run in yet. As the instructions say not to go over 20km/h for the first 500km's.

Steve
 
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cyclepro101

cyclepro101

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OK, here she is. I esspecially like how I made the rear disk brake work. I needed to pack out the disk and file off some of the caliper to get it away from the chain. Also have a very strong connection to the frame now. The new sprocket has made it very smooth and I have also glued a foam mouse pad over the clutch cover and stuffed some cork in the fins and that has made it very very quiet.
 

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Rockenstein

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My bike with a wheel circumference of 2081 mm will hit 45 km/h on flat ground without issue...will cruise at 35 km/h until the fuel supply runs out without missing a beat. Are you sure your speedo is reading correctly? I use an Echo cycle computer and verified it's speed accuracy with one of those road side speed trap signs that was set up near me. The Echo cycle computer allows you to enter the exact numbers for the circumference of the tires I'm using, does your computer\speedometer allow you to do this?

For reference I've got 449 km worth of running on the engine, run a 32:1 mix, engine is unmodified sans the centrifugal clutch, carb needle clip is in the top notch, muffler is lightly packed with 2 stroke muffler wadding, I use an NGK B9HS gaped at .020 and I'm running a 44 tooth gear.


PS: Really liking that disc brake setup, good job man!
 
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cyclepro101

cyclepro101

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OK, I checked my front whell circum. again. It was set at 1940 but a re-ckeck has it at 1947. A small diff so I have fixed that. Its raining here in Aus so I can't check to see if it makes any diff. I am still running 1:16 fuel mix, so maybe with that much oil going through the system it is starving for fuel at the higher revs? Would this be right?
What type of revs do these thing do? Simple (or rather complex math) says that a 26" rear wheel + 10 tooth drive sprocket + 36 tooth rear sprocket + 6000 rpm = 41km/h. And thats what I am getting. Maybe these motors do more than 6000rpm?
Maybe the slight computer adjustment may help out a bit too.

Steve
 
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Rockenstein

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Yea 16:1 is pretty skimpy on the fuel...plenty oil though but oil don't make a big enough bang with regards to peak power output. I noticed a nice difference in power when I went from 20:1 to 32:1...ran 20:1 for the first 4 liters only.
 
cyclepro101

cyclepro101

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Thanks for that. 16:1 compared with 32:1 is a huge diff, so it must be where my top end problems are. Time to lean it down a bit I think.
It must be late over there in the US? Time for bed I think?

Steve
 
Cabinfever1977

Cabinfever1977

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cyclepro that website you listed is from tennessee usa and so they use mph and not kph.
i put in the numbers on the website for a 44t sprocket and it listed 33mph and 44mph for a 36t sprocket @ 6000 rpms. and since i have a 44t sprocket and i can do 32mph+ i would say its maybe right. o and these some of these engines can do more than 6000 rpms. and you say you can go around 45kph which is 27mph,which is ok if you had a 44t sprocket but you have a 36t sprocket.
 
cyclepro101

cyclepro101

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I guess another factor in my top speed could be the fact that I am 230lb's and normally have a 10lb backpack on as well. So the little motor is doing it tuff.

Steve
 
cyclepro101

cyclepro101

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Flat out now she will do about 50km/h (32mph) With a 36t sprocket. I still would of thought she would go faster. But at least it is reving hard at WOT now.
I also put a pair of Kenda K-RAD 3.2 tyres on it that took my wheel circumference from 1947 to 2093.
I have also got a SPB Tuned pipe on the way.

Steve
 
Cabinfever1977

Cabinfever1977

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well you do have to figure in the riders weight,i weigh 120lbs,and if you weigh more you will not go as fast. if i had a 36t sprocket id probally hit 40mph+,as i already can hit 32-35mph with my 44t.

keep working at it and you will get it to how you like it,goodluck.
 
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